In keeping with this issue’s focus on pumps, we are visiting and revisiting some questions we are commonly asked about pump installation and use.

The questions relate to the use of multistage pumps, estimating the cost of operating a pump, making sure that the pump is connected properly to the piping system, watching the piping system to make sure it is not freezing, minimizing solids in lift stations and the impact of solids on pumps.

Multistage issues

Multistage pumps operate at higher heads for lower flow rates. This is advantageous where septic tank effluent is being pumped or on a site with a lot of elevation differences.

These pumps work very well and have been tested to operate for an extremely long time: One manufacturer’s estimate of the average pump life is 12 years. However, these pumps have some specific ­operating characteristics that you need to consider.

The first is that they will handle very few solids — so make sure these pumps are protected from solids. This may mean installing an effluent vault or using these pumps only downstream from a pretreatment system that removes most of the solids from the wastewater.

We have also seen problems where multistage pumps are used with drip-irrigation systems. Since the intake is sometimes located above the motor, and since cooling of the pump to reduce wear depends on the effluent, a 4- to 6-inch slotted PVC pipe (flow inducer) needs to be installed to move effluent past the pump motor to allow cooling.

These are often specified by the manufacturer or designer. If you are installing a flow inducer, remember that, just like any other pump vault, the effluent vault should handle the same gallons per minute your pump will actually deliver during operation.

This is not the same as the design value, which is the minimum flow the pump requires to operate. A quick way to approximate the operating flow is to take the minimum point below the pump curve and draw a 45-degree angle to the pump curve. A much better method is to calibrate the pump at the site.

Cost to operate

Another frequent question, especially now with growing interest in energy savings, is how much it costs to operate a pump. Monthly power consumption in a residential pump station is substantially less than that of major household appliances.

Power consumption varies based on system operating parameters, but you can approximate it using this equation:

Watts X GPD X Days per Month/GPM X 60 min. X 1,000 = kilowatt-hours/month.

Then, multiply the kilowatt-hours per month by the cost of electricity and you have an approximate monthly operating cost. By this calculation, a pump drawing 770 watts and pumping 250 gpd for 30 days at 12.4 gpm would consume 7.76 kilowatt-hours per month. At an electricity price of 10 cents per kilowatt-hour, the pump’s monthly cost would be about 77 cents per month.

Proper connections

We still see many pumps improperly connected to the piping system. First, it is important for the pump to be readily accessible from the surface. This means the pipe must be attached to the pump close enough to the top of the tank under the manhole for a service technician to be able to reach it.

There should also be a quick-disconnect device to allow removal of the pump. This disconnect needs to be something other than a fernco coupling. Using a fernco is not appropriate because of the pressures needed to properly operate the system. (We like to call these “automatic quick-disconnects,” which activate at the most inopportune times.)

Also realize that as the required head or pressure goes up, the pressure on all piping components and connections also increases. This makes it critical to use proper materials. A reminder for people who work in warm weather, or install systems that use STEP designs: If there is a check valve in the system, you should also have an isolation valve to shut the piping off and avoid draining it during the service visit.

Settling and freezing

In cold weather, a chronic problem is the settling and freezing of piping in and around the tank area. This sometimes shows up as a pump that is elevated or hanging at an angle in the pump tank.

The problem is that the backfilling around the piping wasn’t done properly, and the piping has settled to create the dip. The dip is where the freezing is taking place.

The solution has a couple of parts. The first is to backfill in a way that minimizes the pipe’s ability to settle. This includes using proper backfill materials, making sure the trenches are wide enough to enable proper compacting of those materials, and being careful during the backfilling process.

Many cold-weather installers sleeve and protect the supply pipe in a stronger material, often 4-inch Schedule 40 pipe. This material is much stronger than the smaller-diameter supply pipe, and it will keep the pipe from settling during the life of the system.

Another choice would be to run that lighter pipe as much possible on natural ground and then across the lid of the tank to make sure that it has little or no opportunity to settle. However, we do not recommend this because it creates the potential for damaging the piping when the tank is uncovered for servicing.

Solids buildup

The final issue concerns lift stations filling with solids. When this happens, it means the components upstream of the pump tank are not operating properly. There are many possible explanations: lack of maintenance, overloading by the user, or in some cases catastrophic failure of a component.

Because the range of causes is so wide, each needs to be looked at separately. But where solids buildup might cause issues in the pump or downstream components, using some protection in the pump station may be helpful.

An effluent vault or a pump vault may be one of the easier solutions. These technologies protect the pump from drawing in solids, protecting the pump and components downstream.

Another less maintenance-intensive solution would be a bucket surrounding the pump. This raises the elevation of the pump intake, allowing for solids storage in the system. When using this system, be sure to raise the control floats so the bucket will not interfere with the float operation. For example, you can have a significant problem if the “off” float is hung up on a bucket.

These are a few of the issues we encounter regularly in the field. We are sure you run into a number of things as you troubleshoot systems in your neighborhood. We would love to hear about those issues and concerns and, more important, your solutions. We will then share them with others in the onsite industry.